1. Field of the Invention
The present invention relates generally to prosthetic systems for the eye and, more particularly, to an orbital implant for use after evisceration or enucleation of the eye.
2. Discussion of the Background Art
Under certain conditions it is necessary or desirable to remove the human eye because of disease or tissue trauma. Surgical procedures for the removal of an eye, such as evisceration and enucleation, usually include the replacement of the removed eye with a prosthetic system to restore a more normal appearance, maintain the normal structure of the eyelids and eyebrows, and to help stimulate normal growth of the orbital bones in children. The prosthetic system typically includes a sphere for use as an orbital implant and a glass or plastic shell for use as an artificial eye.
After evisceration, the orbital implant is inserted into the residual scleral sac thru a lateral incision to fill the void created by removal of the contents of the eye. In the case of enucleation, the entire eye including the scleral sac is removed, and the orbital implant is inserted directly into the orbital cavity.
Early implantations following enucleation of the eye typically involved closing the orbital cavity around the orbital implant and fitting an artificial eye to the conjunctiva. Because the artificial eye was not connected to the implant, however, realistic tracking of the artificial eye could not be achieved. In fact, even when the artificial eye was somehow connected to the orbital implant, tracking of the artificial eye to the natural eye remained inadequate since the implant merely floated within the orbital cavity. Hence, efforts have been made to attach the ocular motor muscles of the enucleated eye to the implant to produce good tracking of an artificial eye connected to the implant. U.S. Pat. No. 2,667,645 to Moulton, for example, describes the manufacture of a spherical implant from a bio-compatible, synthetic material over part of which is fixed a metal mesh corset. Clips are used to attach some of the ocular motor muscles of the enucleated eye to the metal mesh corset to improve tracking of the artificial eye. In implants employing metallic meshes and clips, however, there is a significant risk of intraorbital trauma and of the implant being rejected. U.S. Pat. No. 5,089,021 thus discloses a spherical core coated with a substantially uniform layer of a microporous, bio-compatible synthetic material such as microporous polytetrafluorethylene, or "GORE-TEX". The synthetic material is intimately mated to the spherical core by adhesive bonding or by stitching which protrudes into the core. The ocular motor muscles may then be attached to the implant with sutures.
In order to avoid the shortcomings associated with materials which are not natural to the human body, it has been proposed in U.S. Pat. No. 4,976,731 to either fill a residual scleral sac after evisceration or, in the case of an enucleation, to place within a scleral sac obtained from a tissue bank, a sphere of low-density, porous hydroxylapatite of the kind obtained from coral or by synthetic means. Hydroxylapatite has the unique biological properties of fully integrating with the surrounding eye tissue while not creating a foreign body reaction or inflammation. It promotes ingrowth by inducing the proliferation of new bone cells (osteocytes), new connective tissue (fibroblasts) and neovascularization and is thus incorporated into the scar tissue and fibro-vascular tissue that develops following surgery. After implantation and recovery, the implant can be drilled or otherwise modified to permit coupling with an artificial eye.
The hydroxylapatite material is expensive, however, and as a consequence of its porosity, tends to fill with fluids in vivo, increasing the weight of the implant. Additionally, procedures for implanting spheres of hydroxylapatite have proven to be time consuming. For example, in the case of enucleation, the hydroxylapatite sphere has typically been wrapped in donor sclera which is difficult to maintain and must be sewn together to form a scleral sac. Furthermore, openings must be formed in the scleral sac by the surgeon immediately prior to inserting the implant into the orbital cavity, in order to expose the hydroxylapatite sphere to the surrounding eye tissue. When used after evisceration, the hydroxylapatite sphere has first been wrapped in a covering to ease insertion and the covering subsequently removed from the scleral sac.
Other disadvantages of known orbital implants include the requirement for a second procedure to drill the implant in order to fit an artificial eye, difficulty in sterilizing the implant material and donor tissue, and the use of complicated and time consuming suturing techniques to cover the implant.